1. Field of the Invention
The present invention relates to the correction of east-west pincushion distortions on the picture screen of a television receiver incorporating a diode modulator, which is controlled by a control stage switched by a line frequency, frame frequency modulated rectangular pulse signal via a coupling coil as well as a diode connected to the coupling coil and which is serving to return stored energy to an electrical energy supply source of the television receiver.
2. Brief Description of the Background of the Invention Including Prior Art
The invention has a starting point a circuit for correcting east-west pincushion distortions on the picture screen of a television receiver with a diode modulator. Such a diode modulator is described for example in detail in the German Patent DE-PS No. 2,031,218. The correction current required for the correction of the above named pincushion distortions is fed to the diode modulator. The diode modulator is here controlled with the aid of a stage, which supplies horizontal scanning frequency rectangular pulses vertically modulated as to their width. It is known to connect a diode to the coupling coil for the return of energy, which diode feeds back energy stored in the coupling coil to an energy supply source of the television receiver. It is known to transform the digital rectangular signal via an RC-member into a parabolic shape signal of frame frequency. It is further known to integrate the digital rectangular signal via an LC-member into a parabolic shape signal of frame frequency which serves to the control stage as negative feedback as well as is fed to the coupling coil for modulating the deflection current.
The first circuit is in fact advantageous from a cost point of view, however it is associated with the disadvantage that the current through the coupling coil during the blocked phase of the control stage can only run in one direction in view of the diode serving to gain energy. Thereby the degree of modulation of the diode modulator circuit is severely limited. This degree of modulation again can be increased by increasing the bridge voltage of the diode modulator, which however reduces the degree of efficiency of the circuit.
The second circuit with the LC-member in fact allows two current directions in the coupling coil based on the capacitor in the integration member such that the full degree of modulation of the diode modulator can be employed. However, this solution is not very advantageous as to costs (German Patent Application Laid Out DE-AS No. 2,809,198) based on the device components employed (inductance and capacitance).
In addition, a circuit provision is known for the correction of east-west distortions of pincushions (German Patent Application Laid Open DE-OS No. 3,124,424), which employs an A-amplifier stage. A modulator circuit generates a sawtooth shaped modulator current with an inductivity, which charges a modulation capacitor. A bias voltage of vertical frequency for the A-amplifier stage changes the shunt current parabolically with the vertical frequency in the direction of an east-west correction. The voltage at the modulation capacitor, which is connected in parallel to the transistor of the amplifier stage, can increase to an undesired size endangering the transistor in case of faulty operating conditions. Therefore, the transistor is clamped via a diode to the voltage of the operating voltage source in order to protect the transistor. The purpose of the diode in this context is to not recover energy back.